When 10g of sodium hydroxide is dissolved in 1000cm3 of water, the sodium formed is approximately [Na = 23, H = 1, O = 16]

When sodium hydroxide (NaOH) is dissolved in water, it dissociates to form sodium ions (Na+) and hydroxide ions (OH-). The balanced chemical equation for this process is: NaOH (s) → Na+ (aq) + OH- (aq) From the question, we are given that 10g of NaOH is dissolved in 1000 cm3 (or 1 dm3) of water. We can calculate the number of moles of NaOH present in the solution using its molar mass: Molar mass of NaOH = 23 + 16 + 1 = 40 g/mol Number of moles of NaOH = mass ÷ molar mass = 10 ÷ 40 = 0.25 mol Since NaOH dissociates to form one Na+ ion for every NaOH molecule, the number of moles of Na+ ions produced is also 0.25 mol. The volume of the solution is 1000 cm3 (or 1 dm3), so the concentration of sodium ions can be calculated as follows: Concentration of Na+ ions = number of moles ÷ volume of solution = 0.25 ÷ 1 = 0.25 mol dm-3 Therefore, the correct answer is "0.25 mol dm-3".